In recent years, unmanned VTOL vehicles have gained importance in various applications suited to their small size and relatively cheap construction. These include aerial videography, search and rescue missions, surveillance, construction, package/food delivery etc. In such UAVs, the multi-rotor arrangement is preferred over conventional single rotor arrangements. The simpler control technique based on varying rotor speeds, bypasses the need for a swashplate mechanism. Small scale UAVs struggle in providing satisfactory performance such as payload, range, and endurance. This is mostly because of higher viscosity-dominated losses at low Reynolds number, and due to yet to be understood rotor-rotor and rotor-airframe aerodynamic interactions.

The focuses is on studying the viscous effects and flow interactions in various multi-rotor arrangements over a range of Reynolds number in hover and forward flight using flow visualization techniques such as high-speed stereo particle image velocimetry (high-speed SPIV), along with thrust, torque and power measurements for rotors. The knowledge acquired through the study will be instrumental in design and optimization of UAVs of possible configurations and scales, improving their performance.